Commercially available high impact polystyrene (HIPS)-like plastics and acrylonitrile-butadiene-styrene (ABS)-like plastics are presently prepared via solution or emulsion techniques wherein polybutadiene rubber is dissolved in a solution of the plastic monomer(s) and graft polymerized onto the rubber. Alternatively, polybutadiene latex is prepared and crosslinked and subsequently, the plastic monomers are grafted onto the latex. From work such as this, it has been established that co-blending of rubber and plastic phases, without grafting or crosslinking does not give good impact strength. Nevertheless, grafting has not been a useful solution for modifying plastics inasmuch as the introduction of graft branches is not readily facilitated or controlled and it has remained difficult to introduce the optimum level of crosslinks by curing.
In order to eliminate the grafting step and also to allow the successful blending of rubber and plastic latices, certain amide containing monomers such as the N-(alkoxymethyl)acrylamides have been utilized in the present invention to form copolymers with both the rubber and plastic monomers. The copolymerization of various amide containing monomers with other monomers is known. One such U.S. Pat. No. 2,925,399, is directed toward a composition formed from a mixture comprising an elastomeric copolymer of butadiene and acrylonitrile with a thermoplastic copolymer of styrene and acrylonitrile. The patent also teaches that the elastomeric copolymers contain at least one further ethylenically unsaturated monomer such as acrylamide or the alkylether of methylol derivatives of acrylamide. Mixing the copolymers disclosed results in products having improved impact strength, although there is no suggestion that a separate monomer be added to both latices, prior to their combination.
U.S. Pat. No. 3,879,495 is directed toward high impact resistance plastics, obtained by polymerizing the plastic in the presence of a rubber. As the plastic segment, an ethylenically unsaturated monomer such as styrene, acrylonitrile, methylmethacrylate, vinyl chloride and N-ethoxymethylacrylamide is selected. Polymerization is conducted in the presence of an olefin-acrylate copolymer as the rubber modifier and, the patent states that the improved properties obtained are attributable to grafting and molecular dispersion.
Providing nitrile resins, stable toward thermal discoloration, is an object of U.S. Pat. No. 4,112,022. The nitrile resins disclosed comprise a copolymer of an .alpha.,.beta.-unsaturated nitrile with a vinyl monomer or, graft copolymers of an .alpha.,.beta.-unsaturated nitrile and a vinyl monomer copolymerizable with a diene rubber and blends of the two, which copolymer is coagulated with an inorganic metal salt. In order to stablize the resin, the addition of an acrylic acid compound is taught among which are disclosed N-(substituted alkyl)acrylamides.
Neither of the latter two patents suggests that the acrylamide containing monomer be copolymerized with the rubber and plastic monomers to form separate latices which can thereafter be blended together. While there are other known techniques for modifying the physical properties of high impact plastics, none are directed to the use of a substituted acrylamide particularly N-(alkoxymethyl)acrylamide, as shall be hereinafter described.